This application relies for priority upon Korean Patent Application No.2000-82829, filed on Dec. 27, 2000, the contents of which are herein incorporated by reference in their entirety.
The present invention relates to a method of forming an insulation layer, and more particularly to a method of forming an insulation layer of a semiconductor device using a spin-on-glass (SOG) layer.
As the elements incorporated into a semiconductor device are increasingly integrated, the sizes of the elements is gradually decreasing, and the semiconductor devices are becoming increasingly multi-layered. Thus, in highly integrated semiconductor devices, problems such as increase in the aspect ratio of contact or via holes which penetrate a given region between the interconnect lines or the circuit elements and enlargement of the step coverage are more intensified. That is, as the aspect ratio of the contact holes is increased, it becomes more difficult to form deep and narrow holes in certain layers of the device and to fill the narrow holes with conductive material to interconnect the multiple layers. Also, undesirable step coverage at a lower part of the device results in a problem when an upper part of the device is patterned to form the interconnects (wires) or elements by means of photolithography. To reduce these problems, a technique using an interlayer insulation layer such as a method of filling gaps between the elements such as gate lines with the interlayer insulation layer and planarizing the upper part of the interlayer insulation layer has been developed and used.
As an example of the technique using an interlayer insulation layer, there has been proposed a method of forming a boro-phospho silicate glass (BPSG) layer and then performing a heat treatment process at a high temperature of about 830xc2x0 C. However, since width between gate lines is designed below a critical dimension (CD) of 0.2 xcexcm with the semiconductor device highly integrated, the heat treatment at the high temperature for forming the interlayer insulation layer may result in a problem damaging the elements, for example reduced transistors in the semiconductor device.
To solve the problem due to the heat treatment at the high temperature, there has been another method of using an O3 tetra ethyl ortho silicate undoped silicate glass (O3 TEOS USG), or high density plasma enhanced chemical vapor deposition (HDP CVD) oxide layer. However, these layers also present a problem of generating voids or seams when the width between gate lines is designed below a CD of 0.2 xcexcm, for example about 0.18 xcexcm.
To solve the problems described above, there has been used another method of using a spin-on glass (SOG) layer as an interlayer insulation layer. SOG materials are advantageous to fill the gaps between the gate lines and to reduce the step coverage since it. is first in a state of liquid or sol.
As one of the SOG materials, hydro silsesquioxane (HSQ) material is used. After the HSQ material is applied to a substrate, a soft bake process is carried out at a low temperature of 100 to 300xc2x0 C. to remove solvent ingredients. Then, a hard bake process is carried out at a temperature of about 400xc2x0 C. for several, e.g., ten, minutes to harden the formed HSQ layer.
However, even though the HSQ layer is annealed under an oxidative atmosphere through the hard bake process, a curing of forming silicon dioxide-crystallized structures is not accomplished well. Particularly, in case of using the SOG layer to fill deep and narrow gaps of the pattern, it is difficult to make oxygen and elements combined thereto diffuse. Also, since the curing is carried out at relatively low temperature and begins from the surface of the SOG layer to interfere with the diffusion of oxygen, the HSQ layer is not cured very well.
When the curing of the HSQ layer is not accomplished well, impurity ingredients such as hydrogen and the like may not be removed completely and remain in the HSQ layer. The impurity ingredients may result in a problem such as forming a porous crystallized structure in the HSQ layer. When the following etching and cleaning process is carried out to a portion of the SOG layer having the porous crystallized structure, an etch rate at the portion of the SOG layer comes to be faster than that at other portions without the porous crystallized structure therein.
For example, in case the interlayer insulation layer is formed of the HSQ layer after forming a metal oxide silicon (MOS) transistor structure on a substrate, the porous structure is apt to be formed in a lower part of the interlayer insulation layer between the gate lines. Therefore, when the pads for bit line contacts or storage node contacts are formed by means of a self-aligned method, the lower part of the SOG layer having the porous structure is exposed. The exposed lower part of the SOG layer is easily etched by a very small amount of etchant contained in a detergent such as a mixture of NH4OH, H2O2, and de-ionized water called SCl, or buffered oxide etcher (BOE). As a result, pipe line shaped bridges can be formed between the adjacent pads through the exposed lower part of the SOG layer. These bridges may cause a short circuit between wires such that the semiconductor device operates abnormally.
Also, in the portion of the SOG layer having the porous structure, a difference in the stress or tension is generated according to the thermal expansion and the like as compared with other portions without the porous structure, to deteriorate reliability of the elements and thereby cause generation of devices of inferior quality.
Among the SOG materials, silazane series is a material indicated as a structural formula xe2x80x94[SiR1R2NR3]nxe2x80x94 having an average atomic weight of 1000 to 2000. The silazane series usually uses perhydro-polysilazane wherein all of R1,R2, and R3 is hydrogen, or organic polysilazane wherein R1,R2, and R3 are alkyl radicals, an aryl radical, and an alkoxyl radical, respectively, containing 1-8 carbon atoms. The perhydro-polysilazane or organic polysilazane which is usually called polysilazane is used in a type of a solution in which it is melted as much as a given % by weight by a solvent such as dibuthyl ether, toluene, or xylene. The polysilazane can be treated by a process of higher temperature as compared with silicate or siloxane series, so that more complete curing can be accomplished. Also, the polysilazane has a high resistance to a wet etching, so that it is easy to apply to the real fabrication process compared with the HSQ layer. Also, when a polysilazane layer is formed to be relatively thick, a plane state of the whole surface of the substrate can be improved enough to carry out the subsequent process steps such as a chemical-mechanical polishing (CMP) without forming a capping oxide layer on an upper part of the polysilazane layer.
The polysilazane layer is generally baked by performing a bake process for removing solvent ingredients, and an annealing process for curing the baked polysilazane layer at a high temperature of more than 600xc2x0 C., for example 700xc2x0 C., after the polysilazane is applied to a substrate. An example of a method of baking and annealing the polysilazane layer is disclosed in Japanese Patent Applicant No. 97-044,132 filed by Nippon Denki Co., Ltd.
FIG. 1 is a flow chart showing the process steps of a conventional method of forming a SOG insulation layer of a semiconductor device. The method comprises forming a pattern on a surface of a substrate (10), applying a SOG layer on the surface of the substrate (20), performing a pre-bake process to the substrate (30), performing a high temperature annealing process to the substrate (40), and performing the subsequent process steps (50).
However, in the method, silane (SiH4) gases which generally begin to discharge from the SOG layer in the vicinity of a temperature of about 400xc2x0 C. are generated in a large quantity during the high temperature annealing process and easily combined with other discharged ingredients such as nitrogen and hydrogen, and an atmosphere gas such as oxygen. Consequently, a plurality of particles composed of silicon oxides or silicon nitrides having magnitudes of several hundred angstroms (xc3x85) are formed on the surface of the substrate and/or in the inside of the equipment. These particles may result in particle defects of the corresponding substrate and/or other substrates in the equipment.
Also, if the particles, for example a particle 21 exists in the substrate before applying the polysilazane, the SOG layer 23 is thickened in the vicinity of the particle 21, as shown by an arrow in FIG. 2. After the high temperature annealing, the thickened portion of the SOG layer 23 is strengthened. Also, a difference in the stress is partially generated according to thermal expansion and the like, so that a crack 25 may be formed in the thickened portion of the SOG layer 23. If the particle or crack occurs in the manufacturing process, the production rate of the semiconductor device will not only be reduced, but also the reliability of the elements will be deteriorated.
Therefore, it is an object of the present invention to provide an improved method of forming an insulation layer of a semiconductor device which when a SOG layer of silazane series is used as the insulation layer, can restrain particles from forming on a surface of a substrate during a high temperature annealing.
It is another object of the present invention to provide an improved method of forming an insulation layer of a semiconductor device which when a SOG layer of silazane series is used as the insulation layer, can prevent cracks from forming due to particles which exists in a substrate before applying the SOG layer.
It is other object of the present invention to provide an improved method of forming an SOG insulation layer of a semiconductor device which can prevent side walls of contact holes from being damaged when a wet cleaning process is carried out after forming the contact holes in the SOG insulation layer.
These and other objects are provided, according to an aspect of the present invention, by a method of forming a SOG insulation layer of a semiconductor device. An SOG insulation layer is formed on a substrate having a stepped pattern using a solution containing polysilazane in an amount of less than 20% by weight in terms of concentration of solid content. A pre-bake process is performed at a temperature of 50 to 350xc2x0 C. to remove solvent ingredients in the insulation layer. The resulting structure is annealed at a temperature of 600 to 1200xc2x0 C.
In one embodiment, the pre-bake process comprises increasing a temperature continuously for 2 to 7 minutes. Alternatively, the pre-bake process can comprise heating at temperatures of 75xc2x0 C., 150xc2x0 C., and 250xc2x0 C. for several minutes, preferably 1 to 2 minutes, each. The pre-bake process is carried out by means of an in-situ method.
In the embodiment, the annealing step is carried out at the temperature of 600 to 1200xc2x0 C. for 10 to 120 minutes, preferably at 700 to 900xc2x0 C. for 30 to 60 minutes. Generally, the more the annealing temperature and time are increased, the more curing is enhanced.
In one embodiment, the solution includes only a polysilazane polymer of a structural formula xe2x80x94[SiR1R2NR3]nxe2x80x94 as the solid content. When the solution includes an addition except the polymer and solvent ingredients, an atomic weight of the polymer can be changed to have influence on the viscosity, so that the thickness and flatness of the SOG layer formed by spin coating can be influenced. Accordingly, it is desirable that the solid content in the solution use only the polysilazane without the additional influence on the viscosity. Preferably, the polysilazane is contained in the solution in an amount of 5 to 15% by weight in terms of concentration of the solid content. When the amount of the polysilazane is below 5% by weight, it is difficult to adjust the thickness of the SOG layer. Particularly, in this case, since the SOG layer is apt to be shallowly formed, it is difficult to apply to the real process. The polysilazane desirably uses a perhydro-polysilazane indicated as a structural formula xe2x80x94[SiH2NH]nxe2x80x94.
The method of the invention can further include forming a CVD insulation layer such as an oxide layer on the SOG layer by means of a CVD method such as a HDP CVD in order to obtain an interlayer insulation layer having a sufficient thickness. Also, the method of the invention can include planarizing the CVD insulation layer by means of a CMP. Thus, in the present invention, the interlayer insulation layer having required characteristics can be formed of the SOG layer and the CVD insulation layer. The SOG layer acts to fill gaps of the pattern and remove the step coverage due to the pattern, and the CVD insulation layer acts to obtain required thickness and reduce the step coverage.
Alternatively, the method of the invention can include performing a hard bake process at a temperature of 350 to 500xc2x0 C. between the pre-bake process and the annealing step. The hard bake process is preferably carried out at a temperature of 400 to 450xc2x0 C. for 30 to 60 minutes under an inert gas or vacuum atmosphere. In the inert gas or vacuum atmosphere, even though gases are generated from the SOG layer, a chemical reaction which forms particles is not activated, so that particles can be restrained from forming during the annealing process. Also, the hard bake process can be carried out under an oxidative atmosphere. In the oxidative atmosphere, since a concentration of the gases which generates during the hard bake process is low, formation of particles is minimal.